Minimum feature sizes of semiconductor devices continue to shrink to enable increasing device densities. One method of achieving such high density patterning is to use thin photoresist films to mitigate problems such pattern collapse of high aspect-ratio resist features upon development. One possible solution to the problem involves using a high-resolution, high sensitivity and high etch durability fullerene resist. However, even though the aspect ratios produced by such resists may be as high as 5:1, the overall etch depth is limited significantly by the usable resist thickness.
A multilayer hard-mask stack can allow a further increase of the aspect ratio of the etched image. Such methods may use a thick amorphous carbon, deposited in—vacuo by chemical vapor deposition, which is then coated with a thin-silicon rich layer. A thin photoresist film is then sufficient to pattern the silicon-rich layer; thus avoiding pattern collapse. The silicon-rich layer is in-turn used as a hard-mask to pattern the carbon, giving a high aspect ratio carbon pattern suitable for providing a mask for etching the silicon wafer. By alternating from silicon to carbon rich materials and vice versa optimization of the overall etch selectivities of various substrates can be accomplished.
In recent years, vapor deposited materials have been replaced with spin-on etch masks. For example, as reported by van Delft et al., J. Vac. Sci. Technol. B, 18 (2000) 3419, a novolak-hydrido silsesquioxane (HSQ) bilayer stack was used to achieve 40 nm half-pitch resolution with an aspect ratio of 3.25:1 as well as isolated 40 nm lines with an aspect ratio of 20:1. However, fluorine-based etching of the underlying HSQ layer, resulted in swelling of the patterned novolak features, leading to wave-like distortions.
Therefore, there remains a need for a spin-on hard-mask material that withstands fluorine-based etching of underlying layers without distortion, so that high resolution patterns can be produced.